Interlocking switch mechanism



May 18, 1937. FQRSTROM 2,080,964

INTERLOCKING SWITCH MECHANISM Filed Oct. 26, 1935 2 Sheets-Sheet 1 A e c p so LOW 18 9s 70 H'GH LOW 1 5 d a x 56 60 $155 62 OFF MED orr OFF 4 1 ss *L I MED MED T;

. I? 52 5 72 HIGH e4 66 76' HIGH 14 r i\:. l.

57 56 gsq 7 52 58 se .62

NVENTOR EDWARD E. FORSTROM BY HIS ATTORNEYS M M M y 1931. E. E. FQRSTROM 2,080,964

INTERLOCKING SWITCH MECHANISM Filed Oct. 26, 1935 2 Sheets-Sheet 2 Low I08 OFF INVENTOR EDWARD E. FORSTROM BY HIS ATTORNEYS WWMM Patented May 18, 1937 I INTERLOCKING swrrcn MECHANISM Edward E. Forstrom, Strattord, Conn., asslgnor to The Bryant Electric Company, Bridgeport, Conn., a corporation of Connecticut Application October 26, 1935, Serial No. 46,944

26 Claims.

This invention relates to mechanical interlocking mechanisms which are particularly adapted for use with electric snap switches of the rotary type. Switches of this type are commonly used for controlling the current flow through resistance units 01' electric stoves, where various degrees of heat must be available totheuser to satisfy the different requirements of use of each unit. My invention finds particular application to the rotary snap switches used on electric stoves but is not limited to such use. Y L

It is desirable when a bank oi. rotary snap switches are used for controlling severally the degrees 01 heat to be given from a number of heating units that not all of the switches be capable of movement into certain positions at one time.

' For example it may be desired to prevent more than one switch moving into the high heat position at one time, since such movement might require the feed lines to carry more than the permissible amount of current, or overtax the power supply.

It is an object of my invention to provide an interlocking mechanism between a plurality of rotary snap switches, which control various heating units of an electric range, by means of which mechanism not more than one of the switches may be placed into high heat position at one time.

Another object of my invention is to provide an interlocking mechanism for rotary snap switches whichcontrol heating units 01' an electric stove or the like by means of which the supply lines may not be compelled to supply more than a predetermined amount of current to the units collectively at any time.

Another object of my invention is to provide an interlocking mechanism between a plurality of switches which control the heating units of an electric stove or the like to permit only one switch to beplaced in position to supply maximum current to its unit at one time, and to permit the remaining switches to supply only a minimum amount or no current to their units at that time.

Another object of my invention is to provide an interlocking mechanism for switches of the above type when the switches are used for controlling the units oi. an electric stove or the like, which mechanism will permit two or more switches to be moved into "medium" or "low heat or ofP position at one time, but which will prevent the movement oi any switch into high heat position when any other switch is in position togive more than low" heat from its heating unit.

Another object of my invention is to provide an interlocking mechanism of the above type which rotary snap switches which will permit the 1 switches to simultaneously occupy medium and low heat positions or 011' position, but will prevent operation of one switch to high heat position when another is in any but of? position.

Other objects and advantages of my invention 1 will become apparent as it is described in connection with the accompanying drawings.

In the drawings:-

Figure 1 is a plan view of an interlocking mechanism constructed according to the principles of my invention, for controlling three rotary snap switches.

Figure 2 is a longitudinal sectional view of the interlocking mechanism shown in Figure l with the section taken on line 4-4 01 Figure 1.

Figure 3 is a plan view of three rotary snap switches mounted upon a plate controlled by an interlocking mechanism constructed according to the principles of my invention.

Figure 4 is a plan view ofanother form of interlocking mechanism constructed according to the principles of my invention for controlling two rotary snap switches.

Figure 5 is a plan view of a third form of interlocking mechanism constructed according to the principles of my invention for controlling three rotary snap switches only one of which may be operated at one time.

Referring to the drawings and particularly to the Figures 1, 2, and 3, thereof it will be noted that three rotary snap switches A, B, and C are mounted upon a rectangular plate P, which may be of sheet metal or sheet insulation or may be part oi an electric stove or other electrical appliance containing conventional heating units fed by the usual supply lines (not shown) and controlled by the three switches A, B, and C.

The switches may be 01' conventional construction and have as many fixed and movable contacts as may be required for controlling a given cir- 5o is in "high" heat position or an intermediate 66 amount of current when the switch is in intermediate or medium heat position, or to give a minimum amount of current when the switch is in low heat position. The fourth position will, of course, be the off position in which no current is transmitted to the heating unit controlled by the particular switch.

Referring to Figure 1 it will be noted that the ends of the spindles 50, 52, and 55 of the switches A, B, and C extend through the mounting plate P and lie in a straight line. Identical cam members designated generally by the numerals 55, 58, 58, and 52 are mounted upon the spindles 55, 52, and 54 as will be apparent by inspection of Figures 1 and 2. It will be noted that cam 55 is mounted upon the spindle 50 and is spaced from the mounting plate P by a collar 51 while cam members 58 and 50 are mounted upon spindle 52, the cam member 50 being spaced from the mounting plate P by a washer 5i and the cam member 58 is spaced from the cam member 60 by an interlocking bar I2, hereinafter described. The cam member 52 is mounted upon the spindle 54 and is spmed from the mounting plate P by a washer 55 of equal thickness to the washer ii. The cams are keyed to the various spindles so as to move therewith.

As before mentioned, the cam members are identical each having a high portion such for example as 56a and a portion of intermediate height as for example 55b and portions of low height such for example as 550 and 55d. The portions 560 and 55d are of equal height and form in effect a single cam surface. The extent of these cam surfaces is in each case less than a 90 are so that each time the switch spindle is rotated from one position to another, a. new surface is presented to interlocking levers 54 and 58, which engage with the cam members as will now be described.

The interlocking lever 58 is bar-shaped, as indicated in Figure 1, having three wide laterally projecting fingers extending from one side at each end and at the middle of the bar. The bar is pivoted at its central portion upon a pivot pin 66 located between the spindles 50 and 52 and slightly to one side of a line through the centers of these spindles. The interlocking lever 68 is similar in plan to the lever 54 and is pivotally mounted upon a pin which is located between the spindles 52 and 54 and slightly to the opposite side of the line through the centers of the spindles from the pivot pin 55. The ends of the interlocking lever 54 are oflset away from the mounting plate P as indicated at 540 in Figure 2, to cause the laterally extending fingers 54a and 54b of interlocking lever 54 to lie in the planes of movement of the cam members 55 and 58. The offsets 58c of the interlocking lever 58 are only of such height as is required to bring the end portions 58a and 58b into the planes of movement of the cam members 55 and 52.

The cams and interlocking levers are also proportioned so that when the high point of one cam is in engagement with one end of an interlocking lever for instance if the high point 55a is in engagement with the end 550, the other end 541) of the interlocking lever 54 will be in engagement with either of the low points of the cam 58. Thus the surface 55 cannot be moved into engagement with the end 54a unless the spindle 52 has been previously moved so as to put either of the low surfaces of the cam 58 into position to be engaged by the end 54b of the lever 5|. Also, the cams are proportioned so that as the end 54a of the interlocking lever 54 rests on the cam surface 55b of intermediate height, the other end 54b may rest on the cam surface of intermediate height of cam 55, as illustrated in Figure 1. A similar situation prevails in connection with the portions of the cams 55 and 52 and the interlocking lever 55. However the movements of the cams and interlocking levers are limited by an interlocking bar 12 which will now be described.

Interconnecting the interlocking lever 54 and 58 is an interlocking bar 12, which is connected with the interlocking lever 54 by a pin I5 which passes through the right hand end of the interlocking lever 55 (see Figure 1) and which is connected with the interlocking lever 55 by a pin passing through the left hand end portion of the interlocking lever 58. There are provided in the end portions of the interlocking bar 12 for the pins 14 and 18, slots 15 and 85 respectively. There is also provided in the interlocking bar 12 for the spindle 52 a slot 52 so that the bar is permitted to have relative movement with respect to the pins 15 and I8 and the spindle 52. The slot 52 is of such extent as to permit the interlocking bar to move on the spindle twice the difference in height between the high cam surfaces and the intermediate cam surfaces of the cam members. This difference, by reason of the proportion of the cams, is equal to the difference between the height of the intermediate cam surfaces and the low cam surfaces of the cam members. The slots 15 and 85 are of such extent as to permit the pins 15 and 18 to move within the slots 15 and 88 each a distance equal to the difference between the high" and medium cam surfaces of the cam members.

From the foregoing it may be ascertained that any one of the switches may be moved into low" or o position from the position shown in Figure 1, that is to say in position to put the cam surfaces of least height such as 550 and 55d beneath the ends of the interlocking levers, for instance. under 55a. This is possible because the movement of the cams to put the low surfaces thereof adjacent the engaging fingers of the interlocking levers does not require any movement of the interlocking levers.

Likewise it may be ascertained that no one of the switches can be moved directly into "high" heat position from the position shown in Figure 1. In order to move the switch A to high heat position, the central cam 55 must be rotated 90 clockwise from the position shown in Figure 1. This can only be accomplished after the cams 58 and 55 (which it will be remembered are movable simultaneously) are moved into either low or 011" position, so as to put the low cam surfaces of these cams, particularly the low cam surface of the cam 58 adjacent the end 54b of the interlocking lever 55. Another condition is requisite before the cam 55 can be moved into high" position, namely the movement of the cam 52 into either low" or of! position so as to put the low surfaces of the cam 52 beneath the cam 55a of interlocking lever 58. This last condition is necessary because the interlocking bar 12, prevents the movement of the interlocking lever 54 counterclockwise from the position shown in Figure 1, until the interlocking lever 58 is permitted to move clockwise to put pin 18 in the outer end of the slot 55. i. e. after the cam 52 has been moved to the "low" or "off" position. It will be apparent upon inspection of Figure 1 that since the pins I4 and I are in the inner ends of slots I0 and 00, movement of the levers 04 and 60 counterclockwise and clockwise respectively must be simultaneous if such movement is initiated by the cam 00.

In order to moveswitch C to high" heat position, switch B will have to be moved to "l'ow or 012", and A will have to be moved to "low or of! just as B and C had to be, in the above description of moving A to high.

In order to move B to "high, both A and C must be moved to low or "off so that low cam surfaces of cams 56 and 02 are adjacent lever fingers 04a and 00a. Then both pins I4 and II can move into the outer ends of slots and 00 of the interlocking bar I2 as the lever fingers 04b and 00b are pushed away from each other by the high points of cams 00 and 00.

when the switch B is in low" or off" position, the interlocking bar I2 prevents both lever fingers 04b and 00b from at the same time engaging the low surfaces of cams 50 and 00 respectively, by reason of the fact that the spacing of the pins 14 and I0 when they are in the inner ends of the slots I0 and 02 is greater than what the spacing of the pins would be while the fingers 04b and 00b were engaging the low surfaces of the earns 50 and 00 if such engagements were simultaneously possible. Since both fingers 04b and 00b can not engage low surfaces of cams 08 and 00 respective-" ly, at the same time, and since such a condition would have to exist if A and C were to be moved into "high" at once, therefore it may be seen that only one of the two switches A or C can be moved into high at one time.

It may also be seen that if switch A or C (A for example) is in "medium position and switch B- is in "off" or low position, still the other switch C, could not move into high" position, because the location of pin 14 in the inner end of the slot 10 of the interlocking bar holds the bar in the same position it occupies in Figure l and prevents the lever 00 from moving counterclockwise from the position of Figure 1 as it would have to do to permit the switch C to move to high.

Below is a table showing all possible positions of the switches.

When A is in: B may be in: C may be in:

Referring to Figure 4, an interlocking mechanism is illustrated for controlling the movements of a pair of rotary snap switches to permit only one switch being put in high" heat position at one time and to prevent the switch from being put in high" heat position when the other switch is in "low", medium' or high" position. In this\ form of the invention, the switches are mounted upon a mounting plate I00 which may be a rectangular piece of metal or sheet insulation or may be a part of an electric range or like device. The ends of the switch spindles I02 and I04 extend through the mounting plate. Fixedly mounted upon the end of the spindle I02 is a cam I06 having a high cam surface I06a, an intermediate cam surface I06!) and another intermediate cam surface I000 merging with the surface I06!) and forming, in effect, a single intermediate cam surface. There is also a low cam surface I06d. The difference in height between the high surface I06a intermediate surfaces I06b and I06c is equal to the difference in height between the intermediate surfaces I00b and I06c and the lower surface I06d. A similar cam I00 is mounted upon the end of the spindle I04. l

For controlling the movement of the cams I06 and I00, there is provided betweenthe spindles a straight, sliding interlocking bar IIO which is provided with a longitudinal central slot H2 in which are the shanks of pins I I4 upon which the interlocking bar is slidably mounted. The ends of the interlocking bar are preferably tapered providing reduced end surfaces 011, Oh which are adapted to engage with the cam surfaces of the cams I06 and I00. The length of the interlocking bar IIO, as measured between the end surfaces IIOa and IIOb, is approximately equal to the distance between the intermediate surface I000 and the intermediate surface I060 when the switch spindle I02 is rotated 90 counterclockwise from the position shown in Figure 4. Thus when the switch I02 is in the position shown in Figure 4, the switch spindle I04 can be rotated from the jlow" heat position in which it is shown in that figure to the 06 or high heats by rotating the spindle 90 or 180 clockwise or the spindle may be rotated into the medium position by rotating it 90 counterclockwise. Thus when the switch spindle I02 is in the off position, the switch I04 may be rotated to any desired position. The converse is true when the spindle I04 is in oif" position. v

When the switch spindle I04 is in the low position as indicated in Figure 4, the switch spindle I02 may be rotated from the ofi position in which it is shown, to the low or medium" heat positions by rotating it 90 or 180 counterclockwise, but it may not be rotated into the high" heat position by rotating 90 clockwise. Since the surfaces I00b and I000 are of equal radius, it will be apparent that the same positions of switch spindle I00 are possible when the switch I04 is in medium position as when it is in low" position. The converse is true as to the possible positions of switch spindle I04 when the switch spindle I02 is in the medium" or low positions.

It will thus be seen that in this form of invention, I have provided an interlocking mechanism which will permit both switches to be moved to medium or low positions at the same time. but when one switch is in high" the other may not be moved from its off position.

Referring now to Figure 5, there is illustrated an interlocking mechanism for three rotary snap switches of the type hereinbefore mentioned. This mechanism permits the movement into active positions of only one switch at a time. In

this form of the invention the switch spindles 202, 204, 206 extend through the mountingplate ly offset from the line joining the spindles, are

a pair of interlocking levers 2, 216. These levers have fingers at each end extending laterally therefrom toward the cams. The fingers 2 Ho, 2 I60, which are at adjacent ends of the levers are of such size as to both be capable of movement into the notch 2 I012. The fingers Zilb and 2l6b are of such width as to occupy substantially the whole of the notches 2081i and H211. Thus when the finger 2 l lb is in the notch 20811 or when 7 the finger M61) is in the notch 2I2-n, the spindle 202 or the spindle 206 can be moved. When both of these fingers are in the notches just mentioned, the switch spindles 202 and 206 will be locked, but the narrow fingers H411 and 2l6a will be withdrawn from the notch H011 and the spindle 204 may be moved freely to any desired position of the switch.

When the narrow finger 2|4a is in the notch Him the switch spindle 202 may be moved freely to any desired position of the switch, since the broad finger 2M1) will then be withdrawn from the notch 2087:. Likewise when the narrow finger M611 is in the notch 2|0n, the long finger 2|6b will be withdrawn from the notch 2|2n and the switch spindle 266 may be moved to any desired position of the switch.

In order to prevent the simultaneous movement of switch spindles 202 and 206, there is provided an interlocking bar 222 which is pivoted upon a pin 224 located equidistant from the spindles 202 and 20S and some distance from the spindle 204 on the same side of the line through the switch spindles as thepivot pins H8 and 220. The bar has end portions engaging with the backs of interlocking levers 2M and H6 at points between the pivot pin H8 and finger 2|4b and between pivot pin 220 and finger 2 I 622 respectively. The bar 222 is proportioned to permit movement of either one or the other outer ends of the interlocking levers 2M and 2| 6 out of the notches 2081i and 2i2n when the finger of the other operating lever is in its notch. The proportioning of the interlocking lever requires that when either the finger 2% or H6 is out of the notch of its cam, then the finger of the other lever 2l6bor 2541) must be in the notch of its cam as shown in Figure 5.

It will thus be apparent that I have provided an interlocking mechanism in which only one of three rotary switches may be operated at one time.

Many changes will occur to those skilled in the art within the scope of my invention, therefore I do not limit the invention to the specific embodiments here shown and described.

I claim:---

1. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an on position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, means including an interlocking member engageable with said cam members and preventing movement of one switch into high heat position when another is in high heat position but permitting at least two switches to occupy low and medium heat positions contemporaneously.

2. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, means including an interlocking member engageable with said cam members and preventing movement of one switch into high heat position or medium heat position when another is in high heat position but permitting at least two switches to occupy low and medium heat positions contemporaneously.

3; In combination with a plurality of rotary electric snap switches each capable 01' occupying high, medium and low heat positions and an 01! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted or movement with the switch spindles, means including an interlocking member engageable with said cam members and preventing movement of one switch into any conducting position when another is in high heat position and permitting movement of at least two switches into low and medium heat positions contemporaneously.

4. In combination with at least three rotary electric snap switches each capable of occupying high, medium and low heat positions and an 0!! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, and means engageable with said cam members for preventing movement of one switch from of! position when another is in any conducting position, said means including an interlocking member.

5. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an off position, and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, a plurality of pivoted levers each cooperating with two of said cam members, and means limiting the movement of said levers to prevent more than one switch being moved into high heat position at one time.

6. In combination with a plurality o! rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, a plurality of pivoted levers each cooperating with two of said cam members, and means cooperating with said levers to prevent one switch from being moved into medium or high position when any other is in high.

7. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an off position and having movable contacts mounted on a switch spindle, an interlockingmechanism comprising cam members mounted for movement with the switch spindles, a plurality I of pivoted levers each cooperating with two of said cam members, and means cooperating with said levers to prevent more than one switch being moved from oil position when any other is in a conducting position.

8. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an 01! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising identical cam members each having three cam surfaces of diiferent heights mounted for movement with said spindles, interlocking means cooperating with said cam members and permitting only one switch to be moved into high heat position at one time but permitting at least two switches to occupy medium and low heat positions contemporaneously.

9. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising identical cam members each having three cam surfaces of different heights mounted for movement with said spindles, interlocking means cooperating with said cam members and preventing any switch from being moved into medium heat position when any other switch is in high heat position but permitting at least two switches to occupy medium and low heat positions contemporaneously.

10. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an off position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising identical cam members each having three cam surfaces of different heights mounted for movement with said spindles, interlocking means cooperating with said cam members and permitting one or more switches to be put into medium heat position at one time but preventing any switch from being put in position to give medium or high heat when any other switch is in high heat position.

11. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil? position and having movable contacts mounted on a switch spindle, and interlocking mechanism comprising cam means mounted for movement with the switch spindles, interlocking means engaging with said cam means, and an interlocking device cooperating with said interlocking means to limit the movement of said interlocking means and prevent more than one switch being moved into high heat position at one time. p

12. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an off position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam means mounted for movement with the switch spindles, interlocking means engaging with said cam means, and an interlocking device cooperating with said interlocking means to limit the movement of said interlocking means and prevent any switch from being moved into medium or high heat position when any other is in high heat position.

13. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an on position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam means mounted for movement with the switch spindles, interlocking means engaging with said cam means, and an interlocking device having a lost-motion connection with said interlocking means, said interlocking mechanism preventing any switch from being moved into high or medium heat position when another is in high heat position.

14. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, pivotally mounted interlocking levers engaging with said cam members and preventing adjacent switches from occupying high heat or medium and high heat positions contemporaneously, and an interlocking device engaging with said levers and preventing any switch from being moved into medium or high heat position when any other is in high or medium heat position. v

15. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil? position and having znovable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, pivotally mounted interlocking levers engaging with said cam members and preventing adjacent switches from occupying conducting positions contemporaneously and an interlocking device engaging with said levers and preventing any switch from occupying aconduct ing position while any other switch occupies a conducting position.

16. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an of! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising identical cam members mounted for movement with the switch spindles, identical pivotally mounted interlocking levers engaging with said cam members and preventing movement of adjacent switches into high heat position contemporaneously or medium and high heat positions contemporaneously, and an interlocking device engaging with said levers and preventing movement of any switch'intohigh heat position when any other is occupying high or medium heat position.

17. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an of! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising identical cam members mounted for movement with the switch spindles, identical pivotally mounted interlocking levers engaging with said cam members and preventing movement of adjacent switches into high heat position contemporaneously or to medium and high heat positions contemporaneously, and an interlocking device having a lost motion connection with said levers and preventing movement of any switch into high heat position when any other is occupying high or medium heat position.

18. In combination with a plurality oi rotary electric snap switches each capable of occupying high, medium and low heat positions and an oi! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, pivotally mounted identical interlocking levers engaging with said cam members and preventing adjacent switches from occupying conducting positions contemporaneously, and a pivoted interlocking device engaging with said levers and preventing any switch from occupying a conducting position when any other switch is in a conducting position.

19. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil position and having movable contacts mounted on a switch spindle, an interlocking-mechanism comprising cam members mounted for movement with the switch spindles, and a slidable member preventing any switch from moving into high heat position when any other is in medium or high heat position but permitting at least two switches to occupy mediumand low heat positions contemporaneously.

20. In combination with at least three rotary I electric snap switches each capable oi occupying high, medium and low heat positions and an oil position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cammembers mounted for movement with the switch spindles, and means engageable with said cam members for preventing movement of one switch into high heat position when another is in high heat position said means ineluding an interlocking member.

21. In combination with at least three rotary electric snap switches each capable of occupying high, medium and low heat positions and an oi! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising one cam member mounted for movement with each switch spindle, and means engageable with said cam members for preventing movement of one switch into high heat position when another is in high heat position said means including an interlocking member.

22. In combination with at least three rotary electric snap switches each capable of occupying high, medium and low heat positions and an off position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mourted for movement with the switch spindles, and means engageable with said cam members for preventing movement of one switch into any conducting position when another is in high heat position said means including an interlocking member.

23. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an ofl position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising identical cam memberseach having three cam surfaces of different heights mounted for movement with said spindles, interlocking means cooperating with said cam members and preventing any switch from being moved into medium heat position when any other switch is in high heat position but permitting movement of any switch into low heat position when another is in high heat position.

24. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an oil position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising identical cam members each having three cam surfaces of diflerent heights mounted for movement with said spindles, interlocking means cooperating with said cam members and preventing any switch from being moved into medium heat position when any other switch is in high heat position but permitting at least two switches to occupy medium and low heat positions contemporaneously and permitting movement of any switch into low heat position when another is in high heat position.

25. In combination with a plurality of rotary electric snap switches each capable oi occupying high, medium and low heat positions and an 01! position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, means including an interlocking member engageable with said cam members and preventing movement of one switch into high heat position when another is in high heat position but permitting movement of any switch into low heat position when another is in high heat position.

26. In combination with a plurality of rotary electric snap switches each capable of occupying high, medium and low heat positions and an ofl position and having movable contacts mounted on a switch spindle, an interlocking mechanism comprising cam members mounted for movement with the switch spindles, means including an interlocking member engageable with said cam members and preventing movement of one switch into high heat position when another is in high heat position but permitting at least two switches to occupy low and medium heat positions contemporaneously and permitting movement of any switch into low heat position when another is in high heat position.

EDWARD E. FORSTROM. 

